Modern transmission networks are composed of a number of interconnected network elements like terminal multiplexers, add/drop multiplexers, crossconnects, and regenerators. Examples of transmission networks are synchronous transmission networks known as SDH or SONET (G.707 10/2000) and optical transport networks (OTN, G.709 02/2001). Such networks serve for the transport of tributary user signals in multiplexed form.
The connection between two physically interconnected network elements in a transmission network is termed section. A section can be monitored for alarm and error conditions. The route a particular tributary signal, also referred to as multiplex unit, takes through a transmission network between source and sink network elements is known as path. In other words, a path is a virtual end-to-end end connection of a multiplex unit through a transmission network. A path can also be monitored from end to end for alarm and error conditions. A tandem connection is defined on a segment of a path and exists for the purpose of alarm and error monitoring, as well. For example, a tandem connection can be transported over a linked sequence of sections on a transmission path. Tandem connections and corresponding source and sink functions are defined in ITU-T G.707, G.709, and G.783, which are incorporated by reference herein.
A problem is that a tandem connection sink which does not receive correct tandem connection information interrupts the path. Therefore, a tandem connection source should not be removed as long as the sink is expecting tandem connection information. On the other hand, a sink without corresponding source should not be activated. Furthermore, the creation of overlapping or nested tandem connections has to be avoided because the new sink or source may disturb an already existing tandem connection and the traffic path.
Activation and deactivation of tandem connections requires a sequence of configuration steps in the network elements where the tandem connection is terminated. The configuration steps in both network elements terminating a tandem connection have therefore to be synchronized in order not to interrupt traffic on a working traffic path. According to ITU-T G.798, which is incorporated by reference herein, a synchronization by the network management system is foreseen. This is, however, complicated, slow, and prone to errors. Moreover, network management interaction requires that both terminating network elements of a tandem connection belong to the same management domain. G.709 also defines a one-byte TCM activation/deactivation field (TCM ACT, TCM: tandem connection monitoring) in the frame overhead but no protocol for activation/deactivation is described and the field is not yet used today.
It is therefore an object of the present invention to provide a method and associated network element for the activation and deactivation of tandem connections without network management intervention.